What is Warfarin? Uses, warnings & side effects

Follow all the prescriber’s instructions when taking this medicine.

Take the dose exactly as prescribed. Doses will change at the beginning and throughout treatment, so make sure you are taking the right dose.

Please read the Medication Guide that comes with the tablets.

Take each day’s dose at the same time every day.

Warfarin tablets can be taken with or without food.

Swallow warfarin tablets whole with a drink of water.

Store warfarin tablets at room temperature, protected from light and moisture.

If a dose of warfarin is forgotten, take it when remembered.

Skip the missed dose if it is almost time for the next dose. Take the next dose at its scheduled time.

Do not take two doses to make up for a missed dose.

Warfarin is not safe for everyone. 

Warfarin is never prescribed to people who:

• Are pregnant

• Have blood disorders, bleeding problems, or certain conditions that cause bleeding

• Have active bleeding, such as ulcers

• Have preeclampsia, eclampsia, or a threatened loss of a fetus

• Are about to undergo certain types of surgery, spinal puncture, lumbar back anesthesia, or other medical procedures that may cause uncontrollable bleeding

• Are experiencing a sudden hazardous spike in blood pressure

• Have signs that they will not take doses correctly

• Have had an allergic reaction to warfarin

The prescriber will need regular blood tests to ensure the dose is correct. At first, these tests are required every day. They will continue on a regular schedule throughout treatment. Keep all appointments.

Tell all doctors, dentists, and other healthcare professionals treating you that you are taking warfarin.

Tell the prescriber when you schedule invasive medical procedures such as dental procedures or surgery.

Carry an ID card at all times indicating that you are taking warfarin.

Before taking warfarin, tell your doctor if you are pregnant, breastfeeding, fall often or have:

• Bleeding problems or a history of bleeding problems

• Kidney problems

• Liver problems

• High blood pressure

• Heart disease

• Congestive heart failure

• Diabetes

Pregnant women cannot safely take warfarin because it will harm the unborn baby. The only exception is women with a mechanical heart valve. The prescriber will ask for a pregnancy test before starting treatment. Immediately tell the prescriber if you become pregnant.

This medicine can cause you to bleed and bruise more easily. Take precautions to avoid injury. Immediately inform the prescriber if you have symptoms of bleeding.

Besides bleeding, warfarin can cause other serious problems, including:

• Kidney damage

• Calcium buildup in small blood vessels

• Skin tissue death

• Sudden release of plaques in the blood vessels

Do not stop taking warfarin until consulting with the prescriber.

Tell the prescriber about all prescription drugs, over-the-counter medications, and supplements being taken not only at the start of therapy but at any time you are taking warfarin, particularly:

• Aspirin

• Nonsteroidal anti-inflammatory drugs (NSAIDs)

• Other blood thinners

• Drugs that break up blood clots called fibrinolytics

• Antidepressants called selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRIs)

• Antibiotics or antifungal medications

• Botanical food supplements or remedies, including garlic, ginkgo, St. John’s wort, co-enzyme Q10, or echinacea

• Foods like leafy green vegetables or grapefruit juice

Make sure other prescribers know you are taking clopidogrel before they prescribe new medications.

Eat a normal and balanced diet. Vitamin K-rich foods such as leafy green vegetables reduce the ability of warfarin to slow down blood clotting. Always talk to the prescriber before making drastic dietary changes.